Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: 5d1761dffb0059dae2de405ab872b7bbd2798576
https://github.com/WebKit/WebKit/commit/5d1761dffb0059dae2de405ab872b7bbd2798576
Author: Sosuke Suzuki <[email protected]>
Date: 2026-09-13 (Sun, 13 Sep 2026)
Changed paths:
A JSTests/stress/string-index-dce-bounds-check.js
M Source/JavaScriptCore/dfg/DFGSSALoweringPhase.cpp
M Source/JavaScriptCore/ftl/FTLLowerDFGToB3.cpp
Log Message:
-----------
[JSC] Extract `CheckInBounds` from `StringAt` and `StringCodePointAt`
https://bugs.webkit.org/show_bug.cgi?id=323640
Reviewed by Yusuke Suzuki.
StringAt and StringCodePointAt speculate that the index is in bounds, and
the abstract interpreter types their result on the strength of that check,
so a user such as `string.codePointAt(index) === undefined` folds to a
constant. The node then has no users left, and MovHintRemoval + DCE in the
FTL pipeline remove it together with its bounds check, so out-of-bounds
indices keep returning the folded constant without exiting.
Extract the bounds check into a CheckInBounds node in SSA lowering, as
existing implementation for StringCharCodeAt. The check survives DCE on its own,
while an unused node stays removable. StringAt with an in-bounds array mode
now checks the index before it is normalized, so a negative index exits
with OutOfBounds and the next compile picks the out-of-bounds mode, which
handles negative indices inline without exiting.
Test: JSTests/stress/string-index-must-generate-dce.js
* JSTests/stress/string-index-dce-bounds-check.js: Added.
(shouldBe):
(codePointAtIsUndefined):
(atIsUndefined):
(charCodeAtIsNaN):
(atNegative):
* Source/JavaScriptCore/dfg/DFGSSALoweringPhase.cpp:
(JSC::DFG::SSALoweringPhase::handleNode):
* Source/JavaScriptCore/ftl/FTLLowerDFGToB3.cpp:
(JSC::FTL::DFG::LowerDFGToB3::compileStringCharAtImpl):
(JSC::FTL::DFG::LowerDFGToB3::compileStringCodePointAt):
Canonical link: https://commits.webkit.org/321014@main
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